US officials said during a visit by the country's top officer to Iraq that Washington was carrying out $12 billion worth of arms and training contracts in Iraq, with the first batch of the 36 F-16 fighter jets Iraq has ordered set to be delivered in September 2014.

Washington agreed last year to sell the F-16s to Baghdad in a multi-billion-dollar deal aimed at increasing the capabilities of Iraq's fledgling air force, a weak point in its national defences.

While Iraq's security forces are regarded as able to maintain internal security, Iraqi and US officials acknowledge they cannot protect Iraq's airspace, borders or territorial waters.

Until last year, when US forces withdrew from Iraq, American troops had helped Baghdad carry out those tasks.